Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 4, 2008) Includes bibliographical references (p. 69-71).

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The sulphation and sulphate decomposition occurring during the oxidation of nickel concentrates were studied by thermal analysis. Samples of industrial nickel concentrates were heated in inert gas to temperatures between 400°C and 850°C and oxidized isothermally in air or in a 4%O2-96%N2 mixture. During isothermal oxidation of the concentrates, SO2 evolved from the roasting reactions led to partial formation of metal sulphates. Following the oxidation and sulphation of the sample, the decomposition of the formed sulphates was studied. This was completed either by heating the sulphated sample to 950°C to thermally decompose the sulphates, or by lowering the partial pressure of oxygen while holding the sample at the isothermal oxidation temperature. The sulphation of the sample was found to follow the parabolic rate law, implying diffusion as the rate controlling-step. The thermal decomposition of the sulphates occurred at a near constant rate, implying zero-order kinetics.

The sulphation and sulphate decomposition occurring during the oxidation of nickel concentrates were studied by thermal analysis. Samples of industrial nickel concentrates were heated in inert gas to temperatures between 400°C and 850°C and oxidized isothermally in air or in a 4%O2-96%N2 mixture. During isothermal oxidation of the concentrates, SO2 evolved from the roasting reactions led to partial formation of metal sulphates. Following the oxidation and sulphation of the sample, the decomposition of the formed sulphates was studied. This was completed either by heating the sulphated sample to 950°C to thermally decompose the sulphates, or by lowering the partial pressure of oxygen while holding the sample at the isothermal oxidation temperature. The sulphation of the sample was found to follow the parabolic rate law, implying diffusion as the rate controlling-step. The thermal decomposition of the sulphates occurred at a near constant rate, implying zero-order kinetics.

The solute strengthening due to oxygen in Zircaloy-2 was investigated over the temperature range 1023 to 1873 K. The flow stress was determined in constant true strain rate hot compression over the strain rate 10('-4)-10('-1)s('-1). In order to provide data for LOCA modelling, the 0 concentration range 1260 to 12360 ppm was investigated. For the single phase (alpha) and (beta) materials, the flow curves were normal, whereas the ((alpha)+(beta)) materials exhibited significant yield drops and strain aging, especially when over 50 vol.% (beta) was present. These effects are attributed to the enrichment of the (beta) phase by the solutes Fe and Cr, which are considered to form ordered zones of the Zr(Fe,Cr)(,2) type in the vicinity of dislocations. The flow stress for both the (alpha) and (beta) Zircaloy-2 obeyed the relationship (sigma) = (sigma)(,0) exp(kc), where (sigma)(,0) and k are constants and c is the wt.% 0. The experimental values indicated that 0 strengthens the (beta) phase less effectively than the (alpha) phase. Rule of mixtures calculations were carried out to predict the flow stresses of the ((alpha)+(beta)) alloys; these agreed reasonably well with the experimental data, as long as due allowance was made for the 0 enrichment and 0 empoverishment of the (alpha) and (beta) phases, respectively. / Within the experimental range, the rate sensitivities increased with temperature from 0.13 to 0.20 and from 0.27 to 0.32 for the fully (alpha) and fully (beta) materials. By contrast, the m vs. T curves for the two-phase materials were marked by a rapid increase in m near the beginning and end of the ((alpha)+(beta)) domain, with a dip at large (beta) fractions, particularly in the high 0 alloys. The dip in rate sensitivity was associated with significant strain aging. The experimental activation energies decreased with stress from 440 to 330 kJ/mol (50 to 140 MPa) and from 150 to 125 kJ/mol (1 to 5 MPa) for the (alpha) and (beta) Zircaloy-2 respectively. The extrapolated zero-stress values of Q increased with 0 concentration from 520 to 570 kJ/mol and from 170 to 260 kJ/mol for the (alpha) and (beta) materials, respectively. These data indicate that high temperature dynamic recovery is easier to activate in the (beta) phase but is more sensitive to oxygen than is (alpha) Zircaloy-2.

Orientador: Rezende Gomes dos Santos / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-09T06:44:12Z (GMT). No. of bitstreams: 1 Rodrigues_JeanRobertPereira_D.pdf: 8469417 bytes, checksum: c6f621d0fa37a4e40a4c2dfa293171d2 (MD5) Previous issue date: 2007 / Resumo: Em operações industriais de fundição, a possibilidade de implantação de uma diversidade de condições operacionais tem como conseqüência a geração de uma ampla gama de estruturas de solidificação que influencia decisivamente nas características mecânicas e na qualidade do produto final. Foi desenvolvida no presente trabalho, por meio de uma seqüência de experimentos, uma análise comparativa do processo de solidificação unidirecional vertical ascendente, em condições transitórias de fluxo de calor, do alumínio comercialmente puro e das ligas Al-Mg com diferentes composições. Esta análise visa investigar experimentalmente o efeito da composição nos principais parâmetros do processo de solidificação e sua influência nas estruturas de solidificação. Após a obtenção dos lingotes e registradas as variações de temperatura, foram determinados os seguintes parâmetros de solidificação: coeficiente de transferência de calor na interface metal/molde, velocidade de avanço da frente de solidificação, gradiente de temperatura em frente à isoterma liquidus, taxa de resfriamento e tempo local de solidificação. São também analisados aspectos relativos a desvios observados na direção preferencial de crescimento durante a solidificação. A análise das macroestruturas obtidas evidencia que a transição colunar/equiaxial é afetada pelo teor de magnésio. É estabelecida no trabalho a dependência dos espaçamentos interdendríticos em relação aos parâmetros de solidificação. Estes espaçamentos dendríticos experimentais referentes a solidificação das ligas Al com 5, 10 e 15%Mg, são usados para estimar por meio de método heurístico a permeabilidade nos canais interdendríticos e também comparados com alguns modelos teóricos de crescimento dendrítico da literatura / Abstract: In industrial casting operations, the possibility of implantation of a diversity of operational conditions has as consequence the generation of a wide range of solidification structures, affecting the mechanical properties and the quality of the final product. It is developed in the present work, applying a sequence of experiments, a comparative analysis of the vertical unidirectional solidification process, under transient heat flow conditions of aluminum commercially pure and Al-Mg alloys with different compositions. This analysis investigate experimentally the effect of the composition in the main solidification parameters and their influence in the structure formation. After obtaining the ingots and registered the temperature variations, the following solidification parameters were obtained: transiet heat transfer coefficients at metal/mold interface, dendrite tip growth rates, thermal gradients, cooling rates and local solidification time. It was also analysed aspects relative to deviations observed in the growth preferential direction during the solidification. The analysis of the obtained microstructures shows that the structure columnar/equiaxed is affected by the magnesium content. It is established in the work the dependence of the interdendritics arm spacings with the solidification parameters and the results were compared with some theoretical models found in the literature. These experimental dendritics arm spacings referring the solidification of Al with 5, 10 and 15 wt % Mg alloys, are used to estimate, applying a heuristic method, the permeability of the interdendritic channels / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Orientador: Amauri Garcia / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-04T03:17:22Z (GMT). No. of bitstreams: 1 Peres_ManoelDiniz_D.pdf: 9910066 bytes, checksum: 05cb5fd7d671ae9a511052bdddd2835e (MD5) Previous issue date: 2005 / Resumo: Foi desenvolvida no presente trabalho uma seqüência de experimentos para analisar a solidificação unidirecional vertical em condições transitórias de fluxo de calor de ligas AI-Si hipoeutéticas. Abordagens teóricas e experimentais são desenvolvidas para a determinação quantitativa de variáveis térmicas de solidificação tais como: coeficientes transitórios de transferência de calor metal/molde; velocidades de deslocamento das isotermas liquidus; taxas de resmamento à frente das isotermas liquidus e tempos locais de solidificação. A análise das macroestruturas obtidas mostra que a transição colunar/equiaxial (TCE) ocorre essencialmente à mesma posição a partir da superficie dos lingotes para todas as ligas examinadas experimentalmente. As variáveis térmicas de solidificação são muito similares na TCE, não sendo possível identificar um critério de transição macroestrutural baseado em apenas uma variável em particular. O trabalho analisa também a dependência dos espaçamentos interdendríticos em relação às variáveis térmicas de solidificação e ao teor de soluto da liga. Estes parâmetros dendríticos experimentais referentes à solidificação das ligas AI 3, 5, 7, 9 % Si, são comparados com os principais modelos teóricos de crescimento dendrítico da literatura / Abstract: Experiments were conducted to analyze the upward unsteady state directional solidification of AI-Si hypoeutectic alloys. A combined theoretical and experimental approach is developed to quantitatively determine solidification thermal variables such as: transient metal/mold heat transfer coefficients, tip growth rates, thermal gradients, tip cooling rates and local solidification time. The observation of the macrostructures has shown that the columnar to equiaxed transition (CET) occurred essentially at the same position from the casting surface for any alloy experimentally examined. The solidification thennal variables are very similar at the CET and it is not possible to identify a structural transition criterion based on a particular variable. The work also focuses on the dependence of dendrite ann spacings on the solidification thermal variables and on alloy solute content. The experimental data concerning the solidification of AI 3, 5, 7 and 9 wt % Si alloys are compared with the main predictive dendritic models from the literature / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

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